Comparison of several G-tolerance measuring methods at various seatback angles

Area of Science:

• Aerospace Medicine
• Human Physiology
• Biomedical Engineering

Background:

• Peripheral light loss (PLL) is the standard endpoint for G-induced blackout during +GZ exposure.
• Assessing G tolerance requires reliable physiological endpoints.

Purpose of the Study:

• To compare the reliability of PLL and temporal artery blood flow cessation as endpoints for G tolerance.
• To evaluate the impact of G onset rate and seatback angle on G tolerance.

Main Methods:

• Eight subjects were exposed to increasing +GZ on a centrifuge at different onset rates (0.1 and 0.3 G/s) and seatback angles (15, 60, 75 degrees).
• Temporal artery blood flow was measured using an ultrasonic Doppler flowmeter.
• Peripheral light loss (PLL), arterial oxygen saturation, respiration, and ECG were also monitored.

Main Results:

• The ultrasonic flowmeter provided reliable G tolerance endpoints in 100% of cases, whereas PLL was reliable in only about 75% of cases.
• G tolerance was slightly higher with a more rapid G onset rate (0.3 G/s).
• Ear oximeter readings for arterial oxygen saturation were variable and delayed, showing minimal changes that increased with G-load duration.

Conclusions:

• Temporal artery blood flow measurement using Doppler ultrasound is a more reliable endpoint for G tolerance than PLL.
• G onset rate influences G tolerance, with faster rates slightly improving tolerance.
• Ear oximetry is less effective for real-time G tolerance assessment compared to blood flow monitoring.